The present invention relates to a process for producing relatively large salt granules of uniform particle size, high purity and excellent crush strength, and also to the resulting salt granules themselves.
While the invention has broad applicability in the production of salt granules, it is particularly useful in providing granules of salts which are useful as fertilizers, especially nitrogen and potassium containing salt granules.
For a variety of reasons the agricultural industry has in recent years turned increasingly to bulk blending techniques for formulating fertilizer blends for field application. Bulk blending involves the mixing of granules of phosphorous containing materials with granules of the other principal fertilizer components, i.e., N and K, to produce a blend especially formulated to meet local needs. Since the fertilizer requirements of a given field will depend upon many circumstances including soil composition, recent crop and fertilizer history, manner of irrigation, etc., it is desirable to custom blend the final fertilizer formulation to suit the desired fertilizer analysis for a given application site.
In order to achieve this objective the agriculture industry has practiced bulk blending on a relatively localized geographical basis. According to this practice, granules containing P, N and K, the three principal fertilizer elements, are separately shipped in bulk to large numbers of bulk blending plants located strategically throughout the agricultural sections of the country.
In order to be useful in such bulk blending operations the granular materials must resist caking during shipping and handling. If the materials do not retain their free flowing properties they cannot be used successfully in the blending equipment used for bulk blending. The granules must also have strength properties, such that the granules can resist breakdown into fine powdered particles during shipping. The reduction of the granules to fine powder during transport results in loss of material and makes it generally impossible to obtain blends of the desired analysis using equipment designed to handle granules of certain specified particle size distribution.
Another important property of granular fertilizer materials suitable for bulk blending and field application is that the size distribution of the granules be closely controlled. Uniform size distribution of all components of the fertilizer is necessary to prevent size segregation in bulk blending equipment and field application equipment.
While the fertilizer industry has been successful in developing processes for producing granules of phosphorous (P) containing materials suitable for use in bulk blending, the industry has been less successful in providing suitable granules of nitrogen (N) and potassium (K) containing materials due to a number of problems.
According to the present invention, a solution to these problems is provided by a unique granulation process which makes available for the first time N and K containing salt particles having purity, strength and particle size properties fully compatible with bulk blending and field application requirements.